Gas chromatography is based on the premise that the combination of analytes making up a sample injected into a column within a gas chromatograph separate as they transverse the column at different rates and subsequently elute from the column at different retention times. Both operational parameters (column head pressure, carrier gas type and oven temperature) and column parameters (length, inside diameter, stationary phase type and thickness) contribute to an analyte's retention time.
It is known how to generate a calibration table of retention times corresponding to identified compounds passing through a column having specified column parameters (that are typically accurate to within 5%) configured in a reference gas chromatograph having a set of specified operating parameters. The retention time table is usually employed for identifying unknowns through analysis on the same system as the calibration table was formed. Also it might be used to assist in the identification of analytes of interest passing through other GC systems configured with a column having the same specified column parameters configured in a GC having the same specified operating parameters. Unfortunately, even slight variations of less than 1% between the reference GC systems column and operating parameters used to form the calibration table, and those of another GC system may result in large variations in retention time. In particular, variations may be due to instrument calibration, atmospheric temperature and pressure changes, oven design, column length and column degradation. Additionally, the accuracy of a table of retention times is subject to both operating and column parameter drift over the many weeks typically required to generate a table (especially if the table is large). Even though it is difficult to replicate exact retention times set forth in a retention time database, such a database is useful in illustrating the relative relationship between retention times such that through trial and error or lengthy cross-correlation, it is possible to positively identify unknown analytes of interest.
A popular "relative retention" approach to using chromatographic databases utilizes retention indices or Kovats indices that circumvent problems in getting the same retention time from instrument-to-instrument, column-to-column. In general, all prior art chromatography calibration table protocols that have been successfully employed for identifying unknown analytes are based on either relative retention times (retention indexes) or retention times related to a specific GC system having specified column and operating parameters that do not change (for example, during column maintenance). Attempts to replicate the identical column and operating parameters on another GC system or after column maintenance, is virtually impossible.
It would be advantageous to develop a method for the identification of analytes of interest by a factor that is not specific to the GC system and/or the column and operating parameters employed for separating the analytes. It would be advantageous to have a method for comparing the separations of samples generated on a number of different GC systems. It would be advantageous to provide for a plurality of individual GC systems optimized for specific purposes (speed, specific analyte, type of detector, column availability etc.) while retaining the ability to reference a single database for analyte identification. It would be advantageous to provide for a generic database that can be easily ported to multiple configurations of instruments including; on-line, fieldable, laboratory, detectors that operate at atmospheric pressure, detectors that operate at a vacuum and those having high resolution.